Various types of lifting platforms guidance systems are known and, frequently, are used as part of sewing machines or other machinery to permit raising and lowering of the machine along a vertical post. A platform is mounted on the post, for which, for example, the sewing machine is secured, the movement along the post permitting depression of the sewing machine for example into a well, so that the sewing machine table can be used for other purposes; or, when raised, to lift the sewing machine to different heights, in accordance with requirements for operation or convenience of the operator. Raising and lowering apparatus of this type may be single-post systems or portal-post systems.
To slide the platform along the post, it has been customary to utilize four ball bearings for each platform-and-post combination, the ball bearings being so located that, in operating condition, they are clamped with a bias force against guide or running surfaces on the post. The posts are usually made of bent or rolled sheet steel. Sewing machines and other machines in which components carry out reciprocating movement are subject to vibrations and oscillations which are transferred via the ball bearings to the post, and from the post to the furniture or furnishing which retains the post in position. Particularly when supporting sewing machines, the transfer of vibration to the support for the sewing machine is undesirable and leads to disturbances in sewing. The ball bearings and the guide surfaces are subject to substantial wear. The high engagement forces which are necessary to press the balls of the ball bearing on the guide surfaces in order to provide positive guidance without play results, in due course, in grooves and striations on the guide surfaces. The reaction forces are transferred over the axes of the ball bearings, and upon formation of grooves or deformation of the guide surfaces, the ball bearing retention elements have to be readjusted. Nevertheless, smooth operation of the carriage and vibration-free retention of the carriage is lost after some operating time.